The intestinal tract is inhabited by a large diverse community of bacteria collectively referred to as the gut microbiota. Alterations in gut microbiota composition are associated with a variety of disease states including obesity, diabetes, and inflammatory bowel disease (IBD). Antibiotics alter host metabolism and transplant of microbiota from diseased persons (or mice) to germfree mice transfers some aspects of disease phenotype, suggesting that altered microbiota may play a role in disease manifestation. There are myriad potential mechanisms by which alterations in gut microbiota might promote disease including increasing energy harvest, production of toxic metabolites, and molecular mimicry of host proteins. Our study of mice with a discrete innate immune deficiency, namely loss of the flagellin receptor toll-like receptor 5 (TLR5), led us to hypothesize that an overarching mechanism by which an aberrant microbiota negatively impacts health is by driving chronic inflammation. More specifically, we hypothesize that the histopathologically-evident gut inflammation that defines IBD is a severe but relatively rare outcome of an altered host-microbiota relationship while a much more common consequence of such disturbances is low-grade inflammation, characterized by elevated proinflammatory gene expression that associates with, and may promote, metabolic syndrome. However, the extent to which altered microbiota are a cause and/or consequence of inflammation, and the mechanisms that mediate this interrelationship remains ill defined. Thus, the overall goal of this proposal is to decipher he interrelationship between microbiota composition, inflammatory signaling, and metabolic syndrome. We utilize WT and TLR5-deficient (T5KO) mice as a highly tractable model in which we can both control and measure microbiota composition and pro-inflammatory signaling. Specifically, we will: 1) Define the role of inflammasome activation in the low-grade inflammation, metabolic syndrome, and gut microbiota alterations in T5KO mice. 2) Determine how loss of TLR5 influences the pro-inflammatory potential of the gut microbiota. 3) Investigate the minimal requirements for T5KO metabolic syndrome. That TLR5- deficient humans may be prone to metabolic syndrome supports the relevance of these mechanistic studies. However, the broader importance of this work is that it will advance understanding of the normal means by which a stable microbiota is maintained and elucidate how alterations in microbiota, irrespective of underlying cause, can promote low-grade inflammation and metabolic syndrome.